1. Field of the Invention
The present invention relates to the field of injection wherein a quantity of an injectable material may be delivered into human or other mammals. More particularly, the invention relates to delivery devices, and the injection of materials therewith, where the quantity of the material delivered by the device must be closely monitored and/or the exact position at which the material enters the body must be closely controlled.
2. Background Art
Injectable materials for human and other mammalian uses are typically injected into the body through a delivery vehicle such as a hypodermic needle. This type of needle is generally a hollow tube terminating at one end in a sharp tip. The needle is typically coupled to one of several known delivery devices which feed to the needle, such as a syringe body (to form a hypodermic syringe), or tubing leading to a bag or other container, in the case of the larger volumes of injectable material.
The hypodermic syringe body provides a stable, sterile environment in which a volume of the injectable material may be held for direct injection through the needle. It also provides a physical platform that an operator, such as a physician or nurse, may grip to control the depth and orientation of the needle during the injection of the injectable material into the human, or other mammalian body. In order to pass the injectable material from the syringe body through the needle, a plunger, having a piston formed on the forward end thereof, is reciprocally received within the syringe body. By pushing the plunger inwardly of the syringe body, the piston is forced inwardly of the syringe body to displace the injectable material in the syringe body through the needle.
One prior art use of hypodermic syringes is as a delivery system for collagen, sold under the trade names Zyplast.RTM. and Zyderm.RTM. by Collagen Corporation, Palo Alto Calif., which may be used for cosmetic or other purposes. In this application, the syringe is used to deliver a quantity of collagen interdermally to eliminate an undesirable cosmetic appearance of the skin at that location. For example, where, as a result of an unrelated surgery, body tissue does not fully support the overlying skin (epidermis), collagen may be injected under the epidermis, deep into the dermis, to provide a supporting mass. Likewise, where an individual has undesired wrinkles which are superficial, collagen may be injected just under the epidermis, to increase the volume of tissue under the epidermis surface to minimize or eliminate the wrinkles.
Using a hypodermic syringe to inject the required amount of collagen at a particular location within the dermis requires a substantial degree of skill. In particular, the practitioner injecting collagen must simultaneously control the depth, orientation and position of the needle at a particular injection site, while providing an inward force on the plunger that is sufficient to force a controlled volumetric flow rate of high viscosity collagen out of the needle and into the exact location in the dermis that will provide the desired cosmetic effect. Each of the individual parameters of plunger force, needle depth, needle orientation and needle position independently contribute to the ultimate cosmetic effect of the injection. However, the structure of a typical hypodermic syringe can make simultaneous control of these different parameters difficult for even skilled practitioners. In particular, to force the collagen through the needle, the practitioner must articulate the thumb of the hand holding the syringe to the back if the rearwardly extending plunger while simultaneously wrapping two or more fingers about the syringe body or over the flange at the back of the syringe body. Then, the practitioner must press the plunger inwardly of the syringe body to physically displace the collagen in the syringe body, and thus, force the collagen out of the needle. As a result, during the period in which the practitioner must exercise precise control over the location of the needle tip, the needle tip is positioned several inches from the nearest portion of the practitioner's hand. Additionally, the syringe effectively pivots about the practitioner's fingers. Therefore, any movement of the practitioner's thumb on the plunger that is not collinear with the plunger will result in an equal and opposite movement of the needle tip. Such movement, when the needle is already positioned at a precise location in the dermis, will move the tip out of position and the collagen will be mis-delivered.
The locating of the needle tip at the proper depth within the dermis is also difficult for the practitioner. To engage the tip of the needle at the proper injection depth, the practitioner may move the needle inwardly and outwardly with respect to the surface of the skin (epidermis). However, there is no visual reference point, other than the end of the syringe body, from which the practitioner can easily determine the extent that the needle extends into the dermis. Thus, the needle tip may be placed too deep, or too shallow, for the intended application. Additionally, as the practitioner depresses the plunger to displace collagen from the needle, the entire syringe may rock back and forth and thus vary the depth of the needle tip at the injection site.
To further complicate the collagen injection regimen, a practitioner typically does not inject a preselected quantity of collagen to create a desired cosmetic effect, but instead typically determines the total injection quantity by monitoring the effect of the injected collagen on the injection site during the injection. As the injection site begins to take on the desired appearance, the practitioner must closely control the quantity of collagen leaving the needle to ensure that the overall quantity of collagen ultimately entering the injection site does not exceed the quantity necessary to provide the desired cosmetic effect. It should be appreciated that the person (practitioner) injecting the collagen must have good, steady control of the fingers, hand and arm and also have excellent eye-hand coordination to be an effective provider of cosmetic collagen injections. These qualities are not always present in individuals, and this has limited the availability of collagen therapy to patients.
In addition to the cosmetic applications for injectable collagen described above, there are newly developed applications for treatment of urinary incontinence and rectal incontinence. These latter applications require delivery of larger quantities of injectable collagen to a precise location within the body. And, although a catheter rather than a needle may be used at the point of injection in some instances (treatment of urinary incontinence for example), accurate delivery of quantity of injectable material is very important.
Therefore, there exists a need in the art to provide a delivery device for materials, including collagen and other injectable materials which provides at least one of the following: (i) improved control over the delivery of the material by the device, including the rate of delivery and the overall quantity of the material delivered; (ii) improved operability, to reduce the effect of the operator's actuation of the syringe plunger on the position of the needle in the dermis for cosmetic applications; and (iii) an easily usable means of determining the depth of penetration of the needle into the dermis for cosmetic applications, to ensure proper delivery of collagen, or other materials, to a desired injection site.